This relates to a snap-on closure adapted for use with a container available as a child-resistant package. More particularly, the improved snap-on closure of the invention has a feature which retains the integrity of the seal and snap-on fitment with the container neck finish while rendering the closure easier to open in the unlocked position of the closure.
Child resistant snap closures are widely known and are of many different varieties. In its simpliest form, such as that disclosed in U.S. Pat. No. 3,627,160, the closure skirt has an inner locking lug adapted to be aligned upon closure rotation with a notch located in an annular locking rib on the neck finish of the container to permit closure removal. In such position, known as the "fire" position, the closure is effectively unlocked to facilitate its removal. The closure skirt likewise has a pair of circumferentially extending snap beads on its inner wall with the midpoint diametrically opposite the lug for snap locking engagement with the annular locking rib. The locking lug lies in the same plane as the locking beads to likewise snap fit beneath the locking rib when the cap is manually pressed down over the container neck.
The closure skirt has an outer finger tab in alignment with the locking lug to provide a bearing surface for the operator's thumb or finger in lifting off the closure when the thumb tab and locking lug are oriented into alignment with the notch in the annular locking rib. Indicia which may be in the form of a triangle serving as a pointer is normally provided on the container neck to indicate when the locking lug is accurately in registry with the notch or gap of the annular locking rib, referred to as the "fire" position.
The closure skirt is relatively stiff and rigid although sufficiently resilient such that it flexes radially outwardly upon closure removal as coacting cam surfaces between the snap beads and the locking rib permit the beads to ride upwardly over the major diameter portion of the locking rib in the process of disengaging the beads from the rib during closure removal in the fire position. The inherent hoop strength offered by the closure skirt limits its resilient expansion thereby rendering the closure oftentimes difficult to remove by especially elderly people or those having finger dexterity or strength problems because of the necessary force required particularly for the removal of small-sized snap-on closures from small-sized containers Because of their smaller size, such closures resist flexing to a greater extent compared to larger-sized closures, hence requiring a greater force to remove from its container.
Also, during closure removal, the locking lug impacts against the outer peripheral edge of the neck finish, despite the unobstructive passage of the locking lug through the notch in the annular locking rib. Since the locking lug is located at a spaced axial distance from the closure end wall, in the same plane as the snap beads so as to underlie the locking rib in the snapped-on position, the lug strikes the upper peripheral edge of the neck finish at the container opening as the closure is tilted upwardly while swinging an arc using the opposite side of the closure as a fulcrum. This impact against the neck finish peripheral edge offers some resistance in the process of closure removal as the lug rides upwardly over such edge. During this process the closure skirt at the finger tab elastically expands radially outwardly as limited by the inherent hoop strength of the skirt.
This resistance may be overcome by those having the strength and finger dexterity to remove the cap in the fire position without much difficulty, although it may present a problem for others.